High-resolution x-ray study of nematic–smectic-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>A</mml:mi></mml:math>and smectic-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>A</mml:mi></mml:math>–reentrant-nematic transitions in liquid-crystal–aerosil gels

Ramazanoglu, M.; Larochelle, S.; Garland, C. W.; Birgeneau, R. J.

doi:10.1103/physreve.77.031702

Cited by 13 publications

(8 citation statements)

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“…Therefore void length scales are formed for the LC molecules which in turn disorder their nematic features creating a random disorder effect on the nematic director. The random pinning effect of nematic director and short range disordered smectic phases were studied extensively for this material by x-ray diffraction techniques [3][4][5][6][10][11][12]. In panel (b) of Fig.…”

Section: Resultsmentioning

confidence: 99%

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Roughness as a measurement of random disorder

Ramazanoglu,

Salci

2017

Preprint

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We have studied the quenched random disorder (QRD) effects created by aerosil dispersion in octylcyanobiphenyl (8CB) liquid crystal (LC) using Atomic Force Microscopy (AFM) technique. Gelation process in the 8CB+aerosil gels yields a QRD network which also changes the surface topography. By increasing the aerosil concentration, the original smooth pattern of LC sample surfaces is suppressed by creating a fractal aerosil surface effect; these surfaces become more porous, rougher with more and bigger crevices. The dispersed aerosil also serves as pinning centers for the liquid crystal molecules. It has been observed that via the diffusion-limited-aggregation process, aerosil nano-particles yield a fractal like surface pattern for the less disordered samples. As the aerosil dispersion increases, the surface can be described by more aggregated regions which also introduce more roughness. Using this fact, we have shown that there is a net correlation between the short-ranged x-ray peak widths (-the results of previous x-ray diffraction experiments-) and the calculated surface roughness. In other words, we have shown that these QRD gels can also be characterized by their surface roughness values.

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Section: Resultsmentioning

confidence: 99%

“…Stoichiometric amounts of 8CB and the aerosil were mixed in high purity ethanol and sonicated at ∼ 300 K for around half an hour. This way high quality 8CB+aerosil mixtures were successfully obtained [6,[10][11][12]. The mixtures were then placed on a hot plate which was held at 310 ±0.5 K constant temperature.…”

Section: Experiments Detailsmentioning

confidence: 99%

Roughness as a measurement of random disorder

Ramazanoglu,

Salci

2017

Preprint

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“…From the point of view of phase transitions and critical phenomena, a large amount of the published work has involved dispersions of aerosils (hydrophillically or hydrophobically treated SiO 2 spherular particles with diameter d ∼ 7 nm) in chiral and nonchiral thermotropic compounds, investigating * nounesis@rrp.demokritos.gr the effects upon the isotropic to nematic (I -N ), N to smectic-A (SmA), SmA to smectic-C (SmC), and SmA to chiral smectic-C (SmC * ) transitions [7][8][9][10][11][12][13][14][15][16][17][18][19]. It has been demonstrated by several studies that aerosils dispersed in LCs lead to the destruction of the quasilong range smectic order even at the very low aerosil concentrations [8].…”

Section: Introductionmentioning

confidence: 99%

CdSe nanoparticles dispersed in ferroelectric smectic liquid crystals: Effects upon the smectic order and the smectic-Ato chiral smectic-Cphase transition

et al. 2013

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Spherical CdSe nanoparticles, surface-treated with oleylamine and tri-octylphosphine, dispersed in ferroelectric liquid crystals, can efficiently target disclination lines, substantially altering the macroscopic properties of the host compound. Here we present an ac calorimetry and x-ray diffraction study demonstrating that for a large range of nanoparticle concentrations the smectic-A layer thickness increases monotonically. This provides evidence for enhanced accumulation of nanoparticles at the smectic layers. Our results for the Smectic-A (SmA) to chiral smectic-C (SmC) phase transition of the liquid crystal S-(+)4-(2'-methylbutyl)phenyl-4'-n-octylbiphenyl-4-carboxylate (CE8) reveal that the character of the transition is profoundly changed as a function of the nanoparticle concentration. Large transition temperature shifts are recorded. Moreover, the heat-capacity peaks exhibit a crossover trend to a step-like anomaly. This behavior may be linked to the weakening of the SmA and SmC order parameter coupling responsible for the observed near-tricritical, mean-field character of the transition in bulk CE8. At lower temperatures, the presence of nanoparticles disrupts the phase sequence involving the tilted hexatic phases most likely by obstructing the establishment of long-range bond-orientational order.

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“…Aerosil nanoparticles dispersed in LC hosts lead to a random network of locally pinned LC molecules, thus they can be used to study the controlled random disorder effects and the associated phase transitions [11][12][13][14][15][16][17][18][19][20][21][22][23]. The electrostatic interaction between the aerosil surface and the polar end of the LC molecules creates pinning forces that perturb the order in the nematic and smectic LC layers (Fig.…”

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“…Since aerosil nanoparticles disrupt the ordered state of LCs, the strength of quenched random disorder in the bulk of 8CB LCs can be controlled by adjusting the aerosil gel density ρ s . This parameter has also been used to characterize the LC+aerosil gel samples [11][12][13][14][15][16][17][18][19][20][21][22]25].…”

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Bulk-boundary correspondence in soft matter

2019

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Bulk-boundary correspondence is the emergence of features at the boundary of a material that are dependent on and yet distinct from the properties of the bulk of the material. The diverse applications of this idea in topological insulators as well as high energy physics prove its universality. However, whether a form of bulk-boundary correspondence holds also in soft matter such as gels, polymers, lipids and other biomaterials is thus far unknown. Aerosil-dispersed liquid crystal gels (LC+aerosil) provide a good testing ground to explore the relation between the controlled variations of the aerosil density within the liquid crystal host bulk and the surface topography of the sample.Here we report on one of the earliest if not the first direct observation of such a correspondence where the controlled strength of random disorder created by aerosil dispersion in the bulk liquid crystal is correlated with the fractal dimension of the surface. We obtained the surface topography of our gel samples with different quenched random disorder strengths by using atomic force microscope techniques, and computed the fractal dimension for each sample. We found that an increase of the aerosil gel density in the bulk corresponds to an increase in the fractal dimension at the surface. From our results emerges a new method to acquire the bulk properties of soft matter such as density, randomness and phase merely from the fractal dimension of the surface.The connection between a material's bulk and its boundary has been one of the guiding principles in several branches of physics in the last decade. The main idea is that the boundary of the system would feature excitations that do not occur in the bulk, yet the physics on the boundary is still determined by the properties of the bulk. For example in topological insulators, the index theorem relates the Chern number quantifying the topology of the insulating bulk to the spectrum of the edge states at the boundary [1][2][3][4]. The holographic principle in high energy physics, also known as gauge/gravity duality, is another example of the bulk-boundary correspondence where the spectrum of the strongly interacting gauge theory in four spacetime dimensions is connected to the weakly interacting theory on the three dimensional boundary via duality [5,6].Here we report on the first ever test of whether bulkboundary correspondence holds in soft condensed matter systems [7,8], particularly in aerosil dispersed liquid crystals ( Fig. 1a). We prepared liquid crystal+aerosil (LC+aerosil) gel mixtures with varying amount of aerosil within, and observed that the aerosil gel density ρ s = m SiO2 /V LC in the bulk is correlated with the fractal dimension of the surface. This experimental verification of the bulk-boundary correspondence in soft matter is the main goal of this study.Liquid crystals (LCs) are not only utilized in screens and TVs, but also used to study phase transitions [9]. Since they possess a rich spectrum of different phases with different types of phase transitions, they stand ou...

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High-resolution x-ray study of nematic–smectic-Aand smectic-A–reentrant-nematic transitions in liquid-crystal–aerosil gels

Cited by 13 publications

References 30 publications

Roughness as a measurement of random disorder

Roughness as a measurement of random disorder

CdSe nanoparticles dispersed in ferroelectric smectic liquid crystals: Effects upon the smectic order and the smectic-Ato chiral smectic-Cphase transition

Bulk-boundary correspondence in soft matter

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